Luckily for president of basketball operations Danny Ainge, he’ll have some time to decompress and ponder his roster decisions, because it would be easy to overreact to the Celtics’ playoff demise.

After Friday night’s 88-80 loss to the Knicks in Game 6 of their Eastern Conference first-round series, Celtics faithful were ready to dispose of Paul Pierce and allow Kevin Garnett to retire in able to move forward. The transition from the Big Three Era to the next era (name to be determined) will be difficult, however, because of salary-cap constraints, lack of expiring contracts, and underachieving players who may be difficult to move.

Before the regular season began, Pierce’s return for the 2013-14 season seemed a foregone conclusion. He was coming off another All-Star season, was the team’s leading scorer, and appeared to have plenty of game left in his seemingly endless tank for two more seasons.

The Knicks exposed Pierce in the series as a turnover-prone, plodding, shot-putting shell of his former self. The question the brass has to answer is whether that was a byproduct of superior defense by Iman Shumpert or whether it was the sign of a swift Pierce decline.

Pierce averaged 18.6 points, 6.3 rebounds, and 4.8 assists per game during the regular season in a career low 33.4 minutes. His shooting percentage dipped to 43.6 primarily because he launched 382 3-pointers, his most since the Big Three Era began.

Pierce has value, but it’s tricky. His cachet around the league may have taken a hit because of his playoff performance. The Celtics have to waive him by June 30 and give him a $5 million buyout or his $15.33 million salary becomes guaranteed.

Ainge should determine what the market is for Pierce, using the player’s experience, talent, and expiring contract as bait. The best-case scenario is to obtain a younger player in the middle of a multiyear deal that a team wants to dump. That is an unusual situation, but it did occur a few months ago when the Grizzlies were looking to deal Rudy Gay and talked with the Celtics. The Celtics didn’t think Gay was a franchise-caliber player and passed on a deal for Pierce.

Ainge also could attempt to pry two players whose salary equals that of Pierce in a trade, but those players likely would be in the middle of multi-year deals, so the Celtics would have to really covet them.

Because of his playoff performance and apparent decline, Pierce’s situation will be delicate, especially if the team decides to amnesty his contract. That would slice his salary off the payroll and push the Celtics near the estimated $59 million cap level. But that would do nothing to create space to sign a premium free agent.

That fact likely would give Ainge encouragement to hold on to Pierce and wait until either the trade deadline or next summer to make the complete break. Ainge is not going to dump Pierce just because of one bad playoff series, but the two may have a serious conversation about a reduced role now that Jeff Green has emerged as the starting small forward.

Expect Ainge to keep Pierce for now, partly out of loyalty but primarily because moving him or cutting ties would bring little in return.

As for Garnett, he appeared exhausted and beleaguered after the season finale but privately gave teammates the impression that he wants to return, especially with Rajon Rondo coming back and a first-round elimination leaving a bad taste.

“You have to deal with him, emotionally, physically, mentally, and then with his talent,” coach Doc Rivers said of Garnett. “It’s amazing when you think about Kevin. He’s, what, 37 [later this month] and he’s still one of the best players in the league and it’s more with his mind. He’s the best.”

Rivers said he had no idea whether Garnett would return, but the future Hall of Famer made it clear his decision is tied to what happens with Pierce. It’s highly unlikely the Celtics would encourage Garnett to retire, and since there is no retirement clause in the collective bargaining agreement, how much of a salary-cap break — if any — the Celtics would receive by Garnett leaving in the middle of a multi-year contract depends on a potential buyout.

As for the rest of the roster, the Celtics have to make more changes. The signing of Courtney Lee and Jason Terry to multi-year deals at $5-plus million may prove salary-cap cloggers, especially since neither emerged as a starting shooting guard. Look for Ainge to shop both contracts, hoping to move at least one. Lee has more value to the Celtics as a reserve and may be more difficult to trade because he has three more years left on his deal.

In return, Ainge wants a capable backup point guard and rebounding center. The club believed it had depth by signing Darko Milicic, whose Celtics tenure lasted five minutes, and Jason Collins, who was reluctantly moved to the Wizards when Boston needed a replacement for Leandro Barbosa.

Depending on what they do with Pierce, the Celtics will have the mini mid-level and minimum contracts to offer and Ainge always could facilitate a sign-and-trade with a team with salary-cap space, as he did with Lee last summer.

Overall, the possibilities are limited. And Ainge will be challenged to upgrade the roster for one more run, to move forward from Pierce and Garnett, or to perhaps part with one and remain competitive. Salary-cap limitations and the new collective bargaining agreement make it impossible for Ainge to deconstruct this roster the way he really wants.

“Nobody feels sorry for us, it does no good for us to feel sorry for ourselves,” Ainge said before Game 5.

“This happens. Basketball injuries happen. We had a couple of tough breaks. It’s my job to always think about the future of the team, but it’s also my job not to talk about the future of our team — until the time is right.”

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